1. Field of the Invention
The present invention relates to a zoom lens barrel.
2. Description of the Related Art
In a known zoom lens camera, a zoom lens barrel has a cam mechanism including a cam ring which is rotatably fitted in a lens barrel block, and a cam follower which is engaged in a cam groove formed in the cam ring, to move a lens group in the optical axis direction in accordance with photographing modes.
For example, in an arrangement in which the cam follower is provided with a pin (radial projection) secured to a lens holder of the lens group and a roller supported by the pin, and the cam groove extends through the thickness of the cam ring, and the roller is not secured; hence there is a chance that the roller may move in the cam groove and be detached from the pin during assembly or during use of the camera.
It is an object of the present invention to provide a zoom lens barrel using a cam mechanism, in which a cam follower is provided with a pin and a roller supported by the pin, wherein no accidental detachment of the roller from the pin takes place.
To achieve the object mentioned above, according to the present invention, a zoom lens barrel is provided, including a through groove which is provided on a first cylindrical member; a radial projection provided on a second cylindrical member which is disposed in the first cylindrical member; and a roller which is supported by the radial projection and is fitted in the through groove. The through groove formed on the first cylindrical member has an opening width on the inner diameter side of the first cylindrical member which is greater than the opening width on the outer diameter side thereof. The roller is provided with an slip-off prevention portion whose diameter is greater than the opening width of the through groove on the outer diameter side but smaller than the opening width on the inner diameter side. The through groove is provided with a large width portion at which the roller is fitted in the through groove from the outside of the first cylindrical member so that the slip-off prevention portion is located in the through groove.
In an embodiment, the through groove is in the form of a non-rectangular sectional shape having a tapered side, wherein the width is gradually increased from the outer diameter side of the first cylindrical member toward the inner diameter side thereof; and the slip-off prevention portion is in the form of a non-rectangular sectional shape having a tapered side, wherein the diameter of the slip-off prevention portion is gradually increased from the outer diameter side of the first cylindrical member toward the inner diameter side thereof, wherein the non-rectangular sectional shape corresponds to the sectional shape of the through groove.
Preferably, a third cylindrical member provided outside the first and second cylindrical members is included, the third cylindrical member being provided with a bottomed groove on the inner peripheral surface thereof whose profile is different from the profile of the through groove of the first cylindrical member. The roller is provided with an engagement portion which has a diameter smaller than the width of the through groove on the outer diameter side of the first cylindrical member and which projects from the through groove and through the outer diameter side to engage with the bottomed groove.
Preferably, the first cylindrical member is a linear movement cylinder which is guided to move in the optical axis direction; the third cylindrical member is a rotary cylinder which is connected to the linear movement cylinder so as to rotate relative thereto but not to relatively move in the optical axis direction; the bottomed groove of the third cylindrical member extends in parallel with the optical axis and the through groove is inclined with respect to the optical axis; and the second cylindrical member is a rotary feed cylinder which is moved in the optical axis direction while rotating in accordance with the profile of the through groove via the rotation of the rotary cylinder.
Upon assembling the roller into the bottomed groove of the third cylindrical member, the roller which is inserted in the through groove of the first cylindrical member through the large width portion is moved to a portion other than the large width portion, so that the roller is engaged in the bottomed groove of the third cylindrical member.
According to another aspect of the present invention, a guiding mechanism for cylindrical members is provided, including a first cylindrical member and a second cylindrical member which is disposed in the first cylindrical member; a through groove formed on the first cylindrical member, the through groove having an opening width on the inner diameter side of the first cylindrical member which is greater than the opening width on the outer diameter side thereof; and a roller which is fitted in the through groove and is supported on a radial projection provided on the second cylindrical member, the roller being provided with an slip-off prevention portion whose diameter is greater than the opening width of the through groove on the outer diameter side of the first cylindrical member and smaller than the opening width on the inner diameter side thereof.
Preferably, the through groove is provided with a partial large width portion at which the roller is fitted in the through groove from the outside of the first cylindrical member so that the slip-off prevention portion is located in the through groove.
In an embodiment, the through groove is in the form of a non-rectangular sectional shape having a tapered side, wherein the width is gradually increased from the outer diameter side of the first cylindrical member toward the inner diameter side thereof; and the slip-off prevention portion is in the form of a non-rectangular sectional shape having a tapered side, wherein the diameter of the slip-off prevention portion is gradually increased from the outer diameter side of the first cylindrical member toward the inner diameter side thereof, wherein the non-rectangular sectional shape corresponds to the sectional shape of the through groove.
Preferably, a third cylindrical member provided outside the first and second cylindrical members is included, the third cylindrical member being provided with a bottomed groove on the inner peripheral surface thereof whose profile is different from the profile of the through groove of the first cylindrical member. The roller is provided with an engagement portion which has a diameter smaller than the width of the through groove on the outer diameter side of the first cylindrical member and which projects from the through groove and through the outer diameter side to engage with the bottomed groove.
Preferably, the first cylindrical member is a linear movement cylinder which is guided to move in the optical axis direction; the third cylindrical member is a rotary cylinder which is connected to the linear movement cylinder so as to rotate relative thereto but not to relatively move in the optical axis direction; the bottomed groove of the third cylindrical member extends in parallel with the optical axis and the through groove is inclined with respect to the optical axis; and the second cylindrical member is a rotary feed cylinder which is moved in the optical axis direction while rotating in accordance with the profile of the through groove via the rotation of the rotary cylinder.
Upon assembling the roller into the bottomed groove of the third cylindrical member, the roller which is inserted in the through groove of the first cylindrical member through the large width portion is moved to a portion other than the large width portion, so that the roller is engaged in the bottomed groove of the third cylindrical member.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 11-323858 (filed on Nov. 15, 1999) which is expressly incorporated herein by reference in its entirety.